Radars typically use high power radio waves and their reflections (radar signals) to determine the range, angle, or velocity of objects. A typical radar system includes a transmitter that generates electromagnetic waves in the radio or microwaves domain, an antenna, a receiver and one or more processors to determine properties of the objects from the transmitted radio waves (pulsed or continuous) reflecting off the object and returning to the receiver.
Currently, radars are being used in many military and commercial fields, such as air and terrestrial traffic control, radar astronomy, air-defense systems, marine radars to locate landmarks and other ships, aircraft anti-collision systems, ocean surveillance systems, outer space surveillance, meteorological precipitation monitoring, altimetry and flight control systems, ground-penetrating radar for geological observations, and range-controlled radar for public health surveillance, among others. Radar signals are typically high frequency (1-100 GHz) signals and therefore generate a substantial amount of electromagnetic power, such as effective radiated power (ERP), which is defined as radio frequency (RF) power, such as that emitted by a radio transmitter. ERP measures the combination of the power emitted by the transmitter and the ability of an antenna to direct that power in a given direction. ERP is equal to the input power to the antenna multiplied by the gain of the antenna. ERP is used in electronics and telecommunications to quantify the apparent power of a transmitting station as experienced by a listening receiver in its reception area.
Similarly, 5th generation (5G) wireless systems, which are the proposed next telecommunications standards, also require a substantial amount of energy.
Typically, radio transmissions require a Federal Communications Commission (FCC) license. However, in recent decades, the FCC has also opened some spectrum bands for unlicensed operations, mostly restricting them to low ERP levels. Nevertheless, unlicensed devices, such as most radio transmission equipment, must still receive technical approval from the FCC before being sold or used, including compliance with FCC power limits. Normally, most of the relevant FCC rules specify power and/or emission limits in terms of the transmitter system (transmitter, radiating antenna, and cable connector) ERP. For example, Table 1 below shows some ERP limits for wireless communications between 450-470 MHz for a specific service area radius.
TABLE 1Maximum ERPService area radius (km)3 8131624324048 6480Maximum ERP (W)2100500500 500 500500500500500
Accordingly, the FCC restricts the utilization of radar and high power wireless communications in commercial spaces (e.g., non-warzones) due to strict limits on ERP of any wireless system. However, many government (e.g., military) and commercial applications (e.g., 5G wireless systems) need to operate radar and communications at high power in these environments.
Current approaches include violating FCC limits with high power wireless transmission, or using low power wireless transmission, which limits the usefulness of the wireless system.